Background: Occasionally, spider bites result in necrotizing soft tissue infections that require aggressive surgical debridement and treatment with intravenous antibiotics. With the rise of microbial resistance in the community, management with standard gram-positive intravenous antibiotic coverage may be ineffective. Our objective was to determine the infectious organisms cultured following wide local excision of soft tissue infections caused by spider bites. We hypothesized that the majority of isolated organisms would be sensitive to penicillin based antibiotics.
Methods: From March 2000 to November 2001, the medical records were reviewed of patients who presented to a tertiary care hospital with serious soft tissue infections secondary to spider bites that required surgical treatment. For each patient, demographics, symptoms, size, time to surgical evaluation (TTSE), temperature, white blood cell (WBC) count, surgical procedure, and culture data were collected. Data are presented as mean +/- SEM.
Results: Thirty-eight patients presented with serious soft tissue infections secondary to spider bites that required surgical debridement and treatment with intravenous antibiotics. Twenty-nine percent (11 of 38) of these patients had failed initial outpatient therapy with penicillin-based oral antibiotics. The mean TTSE was 5.0 +/- 0.5 days (range = 2-14 days; median = 4.5 days). The most common presenting symptoms were pain and erythema surrounding the bite site. The mean temperature was 98.8 +/- 0.6 degrees F (range = 97.2-102.2 degrees F; median = 99.2 degrees F). The mean WBC count was 12.6 +/- 0.8 mm3. All patients required wide surgical debridement of the infected area. The mean size of the excised tissue was 26 +/- 4 cm2 (range = 4-120 cm2; median = 16 cm2). Every patient had cultures that grew Staphylococcus aureus. In 86.8% of patients, S. aureus was found to be methicillin-resistant (MRSA). All isolated organisms were sensitive to trimethoprim-sulfamethoxazole.
Conclusions: In our experience, patients who presented with soft tissue infections as result of spider bites predominantly had methicillin-resistant S. aureus infections, corresponding to the increased incidence of MRSA reported in the community. Therefore, a more aggressive approach to the management of spider bites presenting with severe cellulitis is warranted. Routine treatment should include aggressive surgical debridement, intraoperative wound cultures, the empiric use of antibiotics with activity against MRSA, and adjustment of antimicrobial therapy based on culture and sensitivity data.